Line interface for combining a voice band signal and an XDSL signal on a twisted-pair copper line

Abstract

A line interface for combining a broad-band XDSL signal and a voice-band telephone signal in a copper duplex cable, where the voice-band signal, over and above the voice signal, carries a DC feed for the user telephone and, during the call phase, also a ring signal. The XDSL signal and the voice signal are coupled to at least one primary winding of a line transformer of which the secondary winding pilots the telephone duplex cable. The secondary winding is not DC-coupled with the duplex cable and the ring and feed signals are injected into the duplex cable by a circuit realized in high-voltage technology and arranged in parallel with the secondary winding. A further inductive winding performs the function of compensating the flow variations induced in the core of the line transformer during the call phase.

1 . A line interface for combining a broad-band XDSL signal and a voice-band telephone signal in a twisted-pair copper line, where the voice-band signal, over and above the voice signal, carries a DC feed for the user telephone and, during the call phase, also a ring signal, the XDSL signal and the voice signal being coupled to at least one primary winding of a line transformer of which at least one secondary winding pilots the twisted-pair telephone line, characterized in that said secondary winding is DC decoupled from said telephone line and the ring signals and the feed signals are injected into said line by a circuit arranged in parallel with said secondary winding.  
     
     
         2 . A line interface in accordance with  claim 1 , wherein the DC decoupling of the secondary winding of the line transformer is obtained by means of capacitive decoupling means arranged in series with said secondary winding.  
     
     
         3 . A line interface in accordance with  claim 1 , wherein the capacitive decoupling means comprise at least one capacitor series-connected with the secondary winding in such a manner as to interrupt it at some intermediate point.  
     
     
         4 . A line interface in accordance with  claim 1 , wherein the line transformer comprises at least one further winding to compensate flow variations induced in the core of the line transformer by the ring signal during the call phase.  
     
     
         5 . A line interface in accordance with  claim 4 , wherein the circuit injects the same ring signal into the compensation winding ( 45 ) during the call phase as is injected into the twisted-pair copper line ( 41 ), with amplitude and phase adjusted in such a manners as to eliminate or reduce the flow variations induced in the core ( 44 ) of the line transformer.  
     
     
         6 . A line interface in accordance with  claim 1 , wherein the XDSL signal is filtered by at least one high-pass or band-pass filter ( 24 ) coupled to the primary winding of the line transformer.  
     
     
         7 . A line interface in accordance with  claim 1 , wherein the voice signal is filtered by at least one low-pass filter coupled to the primary winding of the line transformer.  
     
     
         8 . A line interface in accordance with  claim 1 , wherein the XDSL signal and the voice signal are coupled to at least two distinct primary windings ( 38 ,  39 ) of the line transformer.  
     
     
         9 . An interface for driving an XDSL signal and a telephone signal onto a twisted pair, the interface comprising: 
 first and second terminals operable to be coupled to the twisted pair;    a transformer having a first winding operable to be AC coupled to the first and second terminals pair and having a second winding;    an XDSL terminal operable to receive the XDSL signal and coupled to the second winding of the transformer; and    a telephone terminal operable to receive the telephone signal and coupled to the second winding of the transformer.    
     
     
         10 . The interface of  claim 9 , further comprising a capacitor in series with the second winding.  
     
     
         11 . The interface of  claim 10  wherein the capacitor is serially coupled between two portions of the second winding, the two portions having substantially the same length.  
     
     
         12 . The interface of  claim 9 , further comprising a ring-signal generator coupled to the first and second terminals.  
     
     
         13 . The interface of  claim 9 , further comprising a telephone-feed-signal generator coupled to the first and second terminals.  
     
     
         14 . The interface of  claim 9 , further comprising a ring-signal-compensation generator coupled to the second winding of the transformer.  
     
     
         15 . The interface of  claim 9 , further comprising a filter coupled between the XDSL terminal and the second winding, the filter operable to filter out undesirable low-frequency signals from the XDSL signal.  
     
     
         16 . The interface of  claim 9 , further comprising a filter coupled between the telephone terminal and the second winding, the filter operable to filter out undesirable high-frequency signals from the telephone signal.  
     
     
         17 . The interface of  claim 9 , further comprising a synthesizer circuit coupled between the XDSL line and the first primary winding of the transformer core, the synthesizer operable to synthesize the XDSL signal.  
     
     
         18 . The interface of  claim 9 , further comprising a digital-to-analog converter circuit coupled between the XDSL terminal and the second winding of the transformer, the digital-to-analog converter circuit operable to convert the XDSL signal from digital to analog.  
     
     
         19 . The interface of  claim 9 , further comprising a line-driver circuit coupled between the XDSL terminal and the second winding of the transformer, the line-driver circuit operable to amplify the XDSL signal.  
     
     
         20 . The interface of  claim 9 , further comprising a processing circuit coupled between the telephone terminal and the second winding of the transformer, the processing circuit operable to inject a ring compensation signal into the transformer during a call phase.  
     
     
         21 . An interface for driving an XDSL signal and a telephone signal onto a twisted pair, the interface comprising: 
 first and second terminals operable to be coupled to the twisted pair;    a transformer having a first winding operable to be AC coupled to the first and second terminals pair, a second winding, and a third winding;    an XDSL terminal operable to receive the XDSL signal and coupled to the second winding of the transformer; and    a telephone terminal operable to receive the telephone signal and coupled to the third winding of the transformer.    
     
     
         22 . A method, comprising: 
 AC coupling an XDSL signal to a line; and    simultaneously AC coupling a telephone signal to the line.    
     
     
         23 . The method of  claim 22 , further comprising: 
 DC coupling a ring signal to the line during a call phase; and    AC coupling a ring-compensation signal to the line during the call phase.    
     
     
         24 . The method of  claim 23  wherein AC coupling the ring-compensation signal comprises coupling the ring-compensation signal to the line at the initiation of a ring-controller circuit operable to detect the call phase.  
     
     
         25 . The method of  claim 22 , further comprising DC coupling a telephone power signal to the line.